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# Heat Generated by Electrical absorbtion

## Heat Generated by Electrical absorbtion

(OP)
Hi there

Hope you are fine.
Please, I’d like to know if somebody can help me in following topic.

Is there a formula or a rule of thumb that can convert the absorbed power of an electrical equipment to the heat that it produces ?

To make an example:
Let’s assume I have an electrical motor that has a 3.5kW of power consumption.
Is there a rule of thumb to calculate how much of this power is converted in heat ?

Thanks !

### RE: Heat Generated by Electrical absorbtion

Look at the efficiency, everything not turned into output power is heat.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

### RE: Heat Generated by Electrical absorbtion

Depending of equipment type.
For a resistor... sure 100%.
In PC/servers about 90-95% (some mechanical power in internal fans and HDD motors drive).
For a motor, check efficiency in point of load curve; more complicate for variable loads.
Anyway, for small motors (<500W nominal power) about 20%; about 15% in 0.5-5kW range and efficiency increase as nominal motor power increase.

### RE: Heat Generated by Electrical absorbtion

If you're trying to work out (for instance) how much heat you need to extract from a closed compartment with a lot of electrical equipment in it (for instance, a server room) the answer might very well be "all of it" - or slightly more accurately "everything where you can't physically see energy being exported from the space in a pipe, through a turning shaft or shining out through a window".

The proportion of the energy input that actually manages to get converted into mechanical effort, sound or light generally ends up as heat within seconds few anyway and you need to understand whether that heat is something you need to account for or not.

A.

### RE: Heat Generated by Electrical absorbtion

Agree with zeusfaber, unless something leaves the space all of the electrical energy in becomes heat; either immediately or very soon thereafter.

### RE: Heat Generated by Electrical absorbtion

It depends on how efficient the motor is. Most of that energy is going out the motor shaft to perform work. Since the efficiency depends on the load it isn't possible to have a rule of thumb. One needs to look at the particular case.

### RE: Heat Generated by Electrical absorbtion

If the driven load is in the space being considered you have to look at what the load is. For instance if the driven load is a fan that circulates air in the space then all of the electric power eventually all becomes heat; motor efficiency doesn't matter. If you're moving something, product on a conveyor belt, then there is a work component that doesn't become heat.

### RE: Heat Generated by Electrical absorbtion

#### Quote (op)

Let’s assume I have an electrical motor that has a 3.5kW of power consumption.
On what is this assumption based?
Is this measured energy consumed by the motor or is this the nameplate rating of the motor?
The motor will draw enough energy to supply the losses and to drive the load.
The efficiency is stated at full load but the "sweet spot" of highest efficiency is generally around 75% load. As the load drops below the sweet spot, the efficiency drops, even though the losses are dropping also.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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